Hire an Android Developer

The following companies sell beacons that alert users of DROID Phones with a message when they are within 100 yards of the beacon. There are also companies that have DEVELOPED AN APP that ACTS like the beacon device. I am looking for a quote on how much it would cost to use the open source Android platform to create an app that acts like a beacon. The first company listed below has such an app so I know it can be done. The others have just the devices.